1. Field of Invention
The present invention relates to a process for extraction of a carotenoid compound from bacterial cells containing the carotenoid compound.
2. Related Art
Carotenoid compounds are red-yellow series pigments widely distributed in nature, such as in microbial cells, algal cells, and organs and tissues of plants and animals. The carotenoid compounds are used in the field of food additives as coloring agents for foods and beverages, and feed additives for coloring meat or skin of fish such as salmon, trout etc., and for coloring eggs of poultry such as chicken eggs and recently, the use of carotenoid compounds has been expanding. The carotenoid compounds are known to have anti-oxidant action, and are expected to be useful as anti-oxidant agents. In addition, it was recently found that some carotenoid compounds have anti-cancer effect, and therefore are expected to be useful as medicaments.
The carotenoid compounds are classified into those containing an oxygen atom in the molecule and those containing no oxygen atom, and the former are called xanthophyll compounds. Among the xanthophyll compounds, astaxanthin, canthaxanthin, zeaxanthin etc. are industrially produced by chemical synthesis (Pure and Applied Chemistry, 63 (1), 35-44 (1991), and are used as feed additives for coloring.
However, recently it has become difficult to use a chemically synthesized product as food or feed additives due to safety issues, and therefore the development of a process for production of natural carotenoid compounds replacing the chemically synthesized compounds is urgently sought.
For industrial production of carotenoid compounds it is considered that the best process is that comprising culturing bacterial cells to accumulate a carotenoid, recovering the cultured bacterial cells, and extracting the carotenoid compound from the cells, considering the stable supply, high growth rate, high productivity etc.
Japanese Unexamined Patent Publication (Kokai) Nos. 2-138996, 6-165683 and 6-165684 describe methods for extraction of carotenoid compounds from bacterial cells, all of which methods use organic solvents for the extraction. However, since the extracted carotenoid compounds are used as food additives or feed additives, residual solvent may cause problems. Therefore the selection of solvents which can be used for extraction is limited. In addition, xanthophyll compounds which are a group of carotenoid compounds hardly dissolve in solvents which are considered to be safe.